Autonomous vehicular appliance, especially vacuum cleaner

ABSTRACT

Portable threshold locators ( 32 B,  32 C,  32 D) are placed in a room ( 120 ) at locations to define at least part of a boundary within which an autonomous vehicular appliance is to be confined. Typically, the threshold locator is placed in a doorway ( 32 B) or at the top of a staircase ( 32 D). The vehicle has a detection system which allows the autonomous vehicular appliance to detect the presence of the portable threshold locator. The detection system receives a signal from the threshold locator and the autonomous vehicular appliance uses the received signal to avoid the threshold marked by the locator ( 32 B,  32 C,  32 D). The autonomous vehicular appliance is preferably a robotic floor cleaning appliance, such as a robotic vacuum cleaner.

This application claims priority to International Application No.PCT/GB99/04259 which was published on Jun. 29, 2000.

FIELD OF THE INVENTION

This invention relates to an autonomous aplliance, and more particularlyto a robotic floor cleaning device, typically a robotic vacuum cleaner.

BACKGROUND OF THE INVENTION

There has long been a desire for a vacuum cleaner which is capable ofcleaning a room without the need for a human user to push or drag thecleaner around the room. A number of robotic or autonomous vacuumcleaners have been proposed. The control mechanism for these cleanersincludes sensors for detecting obstacles and walls so that the vacuumcleaner is capable of guiding itself around a room so as to clean thecarpet or other floor covering without human intervention. Whileautonomous cleaners are generally capable of dealing with most rooms,there are certain limits on what such cleaners are capable of andautonomous cleaners have been known to struggle in avoiding certaintypes of obstacle in a room. One particularly problematic type ofobstacle is the threshold to a descending stairway. Some autonomouscleaners have been sold with instructions not to use them in roomshaving certain types of feature. Clearly, this limits the usefulness ofan autonomous cleaner.

Some known autonomous floor cleaning devices use navigation beacons ortransponders placed around a room. Signals received at the cleaningdevice from the beacons help the cleaning device determine its positionin the room Typically, the cleaning device determines its positionwithin the room by a triangulation method which uses a signal receivedfrom each of the beacons, The location of the beacons in the room may beknown by the cleaning device in advance or the cleaning device mayestablish their location during a trip around the perimeter of the room.Such beacons are of a high enough power to allow a cleaning device toreceive a signal from each of the beacons, wherever it may be positionedIn the room, A cleaner of this is shown in U.S. Pat. No. 5,682,313(Edlund el al.). The cleaner firstly performs a wall tracking routineusing its ultrasonic sensors and registers the position of thetransponders around the room during this routine. The cleaner issubsequently able to determine its position within the room by using asignal received from each of the transponders and the knowledge of thelocation of the transponders within the room that it has gained duringthe wall tracking routine. The use of an infrared beacon as anavigational aid is shown in U.S. Pat. No. 5,165,064.

EP 0 774 702 describes a boundary detection system for an automatedrobot in which the inner and outer boundaries of a working area aredefined by magnetic markers.

SUMMARY OF THE INVENTION

The present invention seeks to allow an autonomous vehicular applianceto be used in a wider range of environments.

A first aspect of the present invention provides an autonomous vehicularappliance in combination with at least two threshold locators which canbe placed, in use, at locations to define at least part of a boundary ofan area within which the autonomous vehicular appliance is to beconfined at least temporarily, the threshold locators differing in thesignal that they transmit, the appliance being provided with anavigation system for navigating the appliance around the area and adetection system to allow the appliance to detect the presence of thethreshold locators, the detection system comprising means for receivinga signal from a threshold locator and wherein the appliance is arrangedto use the received signal to detect the part of the boundary defined bythe threshold locator and, upon detecting the first threshold locator,to prevent itself from crossing the part of the boundary marked by thethreshold locator and, upon detecting the second threshold locator, toprevent itself from crossing the part of the boundary marked by thethreshold locator until a certain condition has been met.

Other aspects of the present invention provide an autonomous vehicularappliance and a method of cleaning an area using an autonomous vehicularappliance.

The vehicle's own navigation system comprises sensors that allow thevehicle to find features of the room, such as walls and obstacles, andto navigate around the room with respect to these. However, the vehiclemay have difficulty in detecting certain features of the room and inrecognising that these features form part of the boundary of the roomwithin which the vehicle should remain. The threshold locators serve todefine a boundary at these places and allow the vehicle to recognisethat these places should form part of the boundary. This arrangement isparticularly advantageous when the appliance is a robotic floor cleaningdevice and the threshold locators are used to define part of a boundaryof a room which the floor cleaning device should not cross. The portablethreshold locator is typically placed in doorways to confine thecleaning device to a room or at the top of a staircase to prevent thecleaning device falling down the stairs. Without the threshold locator,a doorway will usually be regarded by the cleaning device as an openspace into which it can move. As well as use in defining the perimeterof the room, it can also be used to mark a boundary around obstacleswithin the room which the appliance may otherwise have difficulty indetecting, such as a plant with trailing leaves.

The threshold between areas (rooms) can be marked by using the thresholdlocator which transmits a different signal to the other thresholdlocators. The appliance treats the threshold between areas as one thatshould not be crossed until a certain condition is met. This conditioncan be when the appliance has completely traversed the area.

Use of the threshold locator allows the appliance to be used in roomshaving a much wider range of features or obstacles. Thus, the appliancecan be used in more rooms of a user's home and requires less humansupervision.

BRIEF DESCRIPTION OF THE DRAWINGS

The threshold locators may be permanently installed in a user's home atthe required positions, or they may be used only for the time that thecleaning device is in operation, It is preferable that the locator is ascompact as possible and more preferably takes the form of a strip thatcan be laid as required or conveniently installed beneath a carpet atthe threshold.

The invention will now be more particularly describes, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a robotic floor cleaning device,

FIG. 2 is a circuit diagram of a power management system and anavigation on system for the robotic floor cleaning device shown in FIG.1,

FIG. 3 is a schematic view of one embodiment of a threshold detector anda detection system,

FIG. 4 is a schematic view of another embodiment of a threshold detectorand a detection system;

FIG. 5A is a schematic view illustrating one scenario of operating therobotic floor cleaning device;

FIG. 5B is a schematic view illustrating another scenario of operatingthe robotic floor cleaning device;

FIG. 5C is a more detailed view of the area in FIG. 5B where thethreshold locator is positioned;

FIG. 6 is a flow diagram of a method performed by the autonomous vehicleto detect the presence of a threshold locator; and,

FIG. 7 is a schematic diagram of the functional blocks of the roboticfloor cleaning device which perform the method of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 1 of the drawings, there is shown therein arobotic floor cleaning device in the form of a robotic vacuum cleanercomprising a main body 10, two drive wheels 11 (only one of which isvisible), a brush bar housing 12, two rechargeable batteries 13 and 14,a dual cyclone 15 of the type more fully described in EP-A-0042723, auser interface 16, a light detector 17 and various sensors 27 to 31which will be more particularly described hereinafter. The lightdetector 17 detects light received from a plurality of compass pointsaround the vacuum cleaner and is more fully described in our co-pendingInternational Patent Application No. [our reference GBP0099].

A control system for the cleaner is shown in FIG. 2. The circuitcomprises two rechargeable batteries 13 and 14, a battery and motormanagement system 18, a motor 19 for driving a suction fan, motors 20and 21 for driving the left and right hand wheels 11 of the vacuumcleaner, a motor 22 for driving a brush bar of the vacuum cleaner,processing circuitry 23 and a user interface board 26 with the lightdetector 17, user switches 75 and indicator lamps 76. Preferably theprocessing circuitry includes a microprocessor under the control ofsoftware stored on non-volatile memory 96 and a memory 97 for storingmeasurements from the sensors. A communication bus 70 conveysmeasurement information from the light detector 17 to the processingcircuitry 23.

The robotic vacuum cleaner is equipped with a plurality of infra-redtransmitters 27 a and infra-red receivers 27 b, a plurality ofultrasonic transmitters 28 and ultrasonic receivers 29, one or morethreshold detectors 30 for detecting the presence of a portablethreshold locator 32 placed, for example, at the entrance to a room orat the top of a staircase and one or more passive infrared (PIR) orpyroelectric detectors 31 for detecting animals and fires. There arefour main ultrasonic receivers 29 which face forwards, rearwards and toopposite sides of the robotic vacuum cleaner. The signals received bythese receivers not only provide information representative of distancefrom a feature of the room or from an object in the room but theamplitude and width of the received signals vary according to the sensedsize, shape and type of material of the object.

As shown in FIG. 3, the threshold detector 30 comprises a radiofrequency generator 33 connected to a transmitting coil 34 and areceiver 35 connected to a receiving coil 36.

The portable threshold locator 32 comprises an elongate strip 37 ofplastics material, typically having a length approximately equal to thewidth of a doorway, and a passive circuit 38 for modifying a signalreceived from the threshold detector 30 on the cleaner and fortransmitting the modified signal to the receiving coil 36 on the cleanerwhen the threshold detector 30 is in close proximity to the thresholdlocator 32. As shown, the modifying circuit 38 is in the form of a loopresonator circuit (having a capacitor C and an inductor L connected in aloop) embedded in the strip 37 of plastics material. It is preferablefor the resonance to be distributed along the length of the strip 37 sothat the threshold detector 30 on the cleaner can detect the presence ofthe threshold locator 32 wherever the cleaner may be along the length ofthe strip.

The radio frequency generator 33 periodically produces a radio frequencysignal having a frequency which is the same or substantially the same asthe resonant frequency of the loop resonator circuit 38. This radiofrequency signal may also sweep to either side of the frequency of theresonant circuit 38. When one of the threshold detectors 30 is close toa threshold locator 32, the receiver 35 will receive a weak signal whichis longer than the transmitted signal and this will enable themicroprocessor 23 to identify the presence of the threshold locator 32.Preferably, the transmitter 39 has an antenna gain profile which isrelatively even across the length of the threshold that the thresholdlocator 32 is serving to mark. Similarly to the distributed resonance ofthe passive circuit embodiment, this allows the threshold detector 30 onthe cleaner to detect the presence of the threshold locator 32 whereverthe cleaner may be along the length of the strip, and the more even thegain profile, the more evenly the cleaner will be able to follow theboundary.

In an alternative arrangement, shown in FIG. 4, the portable thresholdlocator 32 could include a signal transmitter 39 powered by arechargeable battery, typically a lithium ion battery 40. In this case,each of the threshold detectors 30 would simply comprise a receiver 41for receiving a signal from the transmitter 39 of the threshold locator32.

In yet a further alternative arrangement, the threshold detector 30could comprise a transmitting coil for generating a magnetic, electricalor electromagnetic field and a receiving coil which will normally pickup the fundamental frequency of the transmitted signal. In this case,the portable threshold locator 32 includes a small piece of metal alloy,or other suitable material, which becomes saturated by the fieldgenerated by the detector 30 when the robotic vacuum cleaner is in closeproximity to the threshold locator 32 and generates an array ofharmonics which are picked up by the receiving coil. The fundamentalfrequency is filtered out leaving low level harmonics which areparticular to the target alloy used. The threshold locator could, inthis case, be in the form of a length of tape.

In each of the embodiments, the cleaner receives a signal from thethreshold locator when the threshold detector of the cleaner is close tothe threshold locator 32. A signal received at the threshold detector issupplied to processing circuitry 23. Various techniques can be used todetermine when the cleaner is close to the threshold locator. Apreferred method monitors a quantity of the received signal and decideswhen the monitored quantity meets a predetermined limit. When themonitored quantity meets this limit, the threshold locator is deemed tobe close enough and the cleaner navigates in a direction to follow apath which maintains the monitored quantity at this limit. The monitoredquantity can be field strength of the received signal and the when themonitored field strength exceeds a predetermined limit, the cleanernavigates in a direction to follow a path of substantially equal fieldstrength.

FIGS. 5A-5C illustrate the way in which the cleaner operates in adomestic environment. Starting with FIG. 5A. the cleaner is, typically,placed alongside a wall (position A) and energised to move forwardlyalong the edge of the room. The various sensors 27 to 31 detect anyportable threshold locators 32A, obstacles in the room and other roomfeatures, such as comers of a room and fireplaces, and the processingcircuitry 23 will navigate the robotic vacuum cleaner in order to avoidany such obstacles and to change direction when a feature of a room isreached. At each change of direction (positions B, C, D), the processingcircuitry 23 stores information received from the light detector 17 andalso from the four main ultrasonic receivers 29. These positions areknown as “waypoints”. It can also store information on the direction inwhich the cleaner turns at each change of direction. It will alsoconstantly monitor the information received from the detector 17 and thefour main receivers 29 and compare this with information previouslystored. When the robotic vacuum cleaner reaches a position in which theinformation received from the light detector 17 and the four mainreceivers 29 is the same or substantially the same as informationpreviously stored, the processing circuitry 23 determines that therobotic vacuum cleaner has completed a complete traverse around the roomand is programmed to cause the robotic vacuum cleaner to step inwards.Preferably, the distance by which the cleaner steps inwardly, the stepdistance, is substantially one cleaner width. On subsequent circuits ofthe room the processing circuitry 23 stores sensor data at changes ofdirection. It associates this with previously stored information byattempting to match the new with the previous information. Two sets ofdata that are sufficiently similar to one another are deemed to bematched and are associated with one another in memory 97. Changes ofdirection on subsequent circuits can be identified by comparing theinformation received from the light detector 17 and the four mainreceivers 29 with previously stored information to allow the roboticvacuum cleaner to navigate itself around the room avoiding any obstaclesin its path in a generally inwardly spiral manner. The sensorinformation from waypoints (B, C, D, E.) visited by the cleaner arestored in a waypoint database, stored in memory 97.

This operating method is more particularly described in our co-pendingInternational Patent Application No. [our reference GBP0100]. However,other strategies can equally be used to navigate around the room.

If the robotic vacuum cleaner is initially placed in the middle of theroom, it will find a wall or obstacle. If it finds a wall it will thenfollow the path described above. If it finds a feature (such as acentral fireplace) or an obstacle in the centre of the room, it willcomplete a circuit around that feature or obstacle and then follow agenerally outwardly spiral path.

FIG. 5B shows another scenario in which the cleaner is operated. A userhas placed threshold locators 32B, 32C, 32D in the room 120 to mark theboundary of the area within which the cleaner is to be confined. Locator32B lies across the threshold of an open doorway to prevent the cleanerfrom escaping into room 122. Locators 32C are placed around a plantwhich is a difficult object for the cleaner to properly detect, thelocators 32C clearly marking a boundary for the cleaner. Locator 32D isplaced along the threshold of a descending stairway. In use, the cleaneroperates within the area defined by the walls of the room 120 and thethreshold locators 32B, 32C, 32D. The outermost path of the cleaner inroom 120 is shown by line 130. Preferably, threshold locator 32B, whichmarks the boundary between rooms 120 and 122, has a special identitywhich can be recognised by the cleaner. Where the threshold locator is apassive resonant circuit, the special identity can be a response at aresonant frequency which is different from the resonant frequencygenerated by the other threshold locators 32C, 32D. The cleaner can beprogrammed to operate so that it firstly regards the threshold marked bythreshold locator 32B as a part of the boundary which should not becrossed. Once the cleaner has completely traversed the floor area inroom 120, it can then cross the threshold marked by threshold locator32B and move into room 122. The cleaner uses an appropriate method toestablish when the room 120 has been completely traversed. One preferredmethod operates the cleaner to cover the floor area in a generallyinwardly spiralling manner towards the centre of the room, the cleanerstepping inwardly after each circuit of the room and determining that ithas completely traversed the room when it has reached the centre of theroom. Upon determining that the room has been completely traversed, thecleaner navigates itself to the threshold locator that marks thethreshold to entering the adjacent room 122. Threshold locator 32Bcarries some form of identification to allow a user to recognise thislocator as one that should be used at the threshold between rooms, suchas text marking.

FIG. 6 shows a flow diagram of a preferred method performed by thecleaner to detect the presence of a threshold locator and FIG. 7schematically shows the functional blocks of the cleaner which performthis method.

Threshold detector 30 provides an output which is representative of thefield generated by the threshold locator. As described above, this fieldcan generated by a passive resonant circuit at the locator 32 inresponse to an exciting signal generated by the cleaner. A fieldstrength monitor function 80 receives the signal from the thresholddetector hardware (typically a receive coil and an amplifier) andconverts this into a value indicative of the received field strength.This can be achieved by using an analogue to digital converter. Thisactivity is shown as step 200 in FIG. 6.

The field strength value is compared with a limit by a comparisonfunction 81. When the field strength of the received signal exceeds thelimit, then a threshold locator is deemed to be present close to thecleaner and a control signal is sent to the navigation system 90 (step202).

The navigation system then navigates the cleaner along a path around thethreshold locator. It achieves this by receiving the output of the fieldstrength monitor 80 and steering the cleaner so as to maintain thereceived field strength at a predetermined limit (step 204).

The navigation system 90 sends control signals to traction motors 20,21. In order to detect when the cleaner has passed the threshold, thenavigation system continues to receive inputs from its other sensors.,the infra-red 27 a, 27 b and ultrasonic sensors 28, 29, and determineswhen a room feature reappears that the cleaner can track. (Step 206).When a room feature is detected, the cleaner continues navigation aroundthe room in a normal manner. (Step 208).

The path of the cleaner around the threshold locator 32B is shown indetail in FIG. 5C. As previously described, a preferred method ofnavigating the cleaner around a room is based on storing measurementsfrom the on-board sensors whenever the cleaner reaches a room feature,known as “waypoints”. As the cleaner travels around the perimeter of theroom, it stores waypoints at room features where the cleaner is forcedto change direction. The cleaner follows a path which is parallel andclose to the wall 110 (path 100). At position 101 the cleaner attemptsto follow the wall as the cleaner considers the door frame to be acontinuation of the wall. However, the threshold detector detects thepresence of the threshold locator 32B and the navigation system stopsits normal wall-tracking operation. Instead, the cleaner follows a pathwhich is generally parallel path to the edge of the threshold locator32B (102) until the cleaner reaches point 103 where the other sensorsdetect the presence of the door frame and wall (112). When the cleanerfirst detects the presence of a threshold locator (position 101) ittakes a waypoint, i.e. it stores measurements from on-board sensors. Onsubsequent circuits of the room, when the cleaner is travelling aroundthe room at a distance inwardly from the perimeter of the room (known asa scan distance), the cleaner may not be able to directly detect thepresence of the threshold locator. Passive resonant circuits can only bedetected when the exciting coil on the cleaner and the resonant coil onthe threshold locator 32 are closely located to one another. On asubsequent circuit of the room (path 105, FIG. 5C) the cleaner detectsthe edge of wall 110. Two alternative ways of operating the cleaner onsubsequent circuits will now be described.

In the first method, the cleaner takes a waypoint at point 106 upondetecting the edge of wall 110. By comparing the data at this newwaypoint 106 with previously stored data, it finds that the new datamatches the data for position 101. It knows, from the record in waypointdatabase, that point 101 represents the start of a part of the boundaryof the room that is marked by threshold locator 32B. Therefore, thecleaner continues to move forward (direction 107) rather than attemptingto follow the physical boundary of the room (wall 110). If necessary,the cleaner can detect the presence of wall 112 at position 108, take awaypoint, and by matching, can match this with the data taken atposition 103 which the cleaner knows is the end of the boundary markedby the threshold locator 32B.

In an alternative method, upon detecting the edge of wall 110 at point106, the cleaner tracks the wall 110 to arrive at point 101 where itdetects threshold locator 32B. The cleaner then moves along the boundarydefined by the threshold locator 32B in the same manner as previouslydescribed for the perimeter circuit until, at point 103 it detects thewall and moves inwardly to resume a circuit of the room at the same scandistance at which the cleaner was previously operating.

In the schematic diagram of FIG. 7, the field strength monitor 80,comparison function 81 and navigation system 90 can all be realised assoftware running on the processing circuitry 23 (FIG. 2).

What is claimed is:
 1. An autonomous vehicular appliance, comprising atleast two types of threshold locators having differing transmittingsignals and being capable of defining at least part of a boundary of anarea within which the autonomous vehicular appliance is to be confinedat least temporarily, a navigation system for navigating the appliancearound the area and a detection system to allow the appliance to detectthe presence of the threshold locators, the detection system comprisingmeans for receiving a signal from at least one each of the two types ofthreshold locators, and wherein the appliance is configured to use areceived signal to detect parts of the boundary defined by the thresholdlocators, and upon detecting a first type of threshold locator, toprevent itself from crossing the part of the boundary marked by thefirst type of threshold locator and, upon detecting a second type ofthreshold locator, to prevent itself from crossing the part of theboundary marked by the second type of threshold locator until a certaincondition has been met.
 2. The appliance according to claim 1, whereinthe appliance is configured, upon detecting the second type of thresholdlocator, to prevent itself from crossing the part of the boundary markedby the threshold locator until the area has been completely traversed bythe appliance.
 3. The appliance according to claim 2, wherein the secondtype of threshold locator transmits a signal which is indicative ofmarking a threshold to another area.
 4. The appliance according to claim1, wherein the autonomous vehicular appliance includes a signaltransmitter and a signal receiver and the threshold locator includesmeans for modifying a signal received from the signal transmitter andfor transmitting the modified signal to the signal receiver.
 5. Theappliance according to claim 4, wherein the modifying means includes apassive circuit.
 6. The appliance according to claim 5, wherein thepassive circuit is a loop resonator circuit and the signal transmitteris arranged to transmit a signal at or close to the resonant frequencyof the loop resonator circuit.
 7. The appliance according to claim 6,wherein the threshold locator is elongate and the resonant circuit isdistributed along the length of the locator.
 8. The appliance accordingto claim 4, wherein the transmitter generates a magnetic signal and themodifying means includes a metal alloy.
 9. The appliance according toclaim 1, wherein the threshold detector includes a signal transmitterand the autonomous vehicular appliance includes a signal receiver. 10.The appliance according to claim 1 wherein the navigation systemincludes a light detector for detecting the level of ambient light,memory means for storing information representative of the level ofambient light when the autonomous vehicular appliance changes directionand means for comparing the level of ambient light with previouslystored information so that the autonomous vehicular appliance canidentify when the level of ambient light is the same or substantiallythe same as a level previously stored.
 11. The appliance according toclaim 1, wherein the navigation system also comprises a plurality ofsensors for detecting obstacles and features of the room.
 12. Theappliance according to claim 1, wherein the detection system comprisesmeans for detecting when a parameter of the received signal meets arequired condition.
 13. The appliance according to claim 1, whereindetection system comprises means for detecting when the field strengthof the received signals exceeds a predetermined limit.
 14. The applianceaccording to claim 13, wherein, upon detecting that the field strengthof the received signals exceeds a predetermined limit, the navigationsystem is configured to navigate the appliance in a direction to followa path of substantially equal field strength.
 15. An autonomousvehicular appliance, comprising a navigation system for navigating theappliance around an area and a detection system to allow the applianceto detect the presence of at least two types of portable thresholdlocators having different transmitting signals and capable of definingat least part of a boundary of an area within which the autonomousvehicular appliance is to be confined at least temporarily, thedetection system comprising means for receiving signals from at leasttwo types of threshold locator and wherein the appliance is configuredto use the received signals to detect the parts of the boundary definedby the threshold locators, and upon detecting a first type of thresholdlocator, to prevent itself from crossing the part of the boundary markedby the first type of threshold locator and, upon detecting a second typeof threshold locator, to prevent itself from crossing the part of theboundary marked by the second type of threshold locator until a certaincondition has been met.
 16. An autonomous vehicular appliance accordingto claim 15, which is configured to prevent itself from crossing thepart of the boundary marked by the second type of threshold locatoruntil the area has been completely traversed by the appliance.
 17. Anautonomous vehicular appliance according to claim 15, further comprisinga signal transmitter for transmitting signals to the threshold locatorsand a signal receiver for receiving signals from the threshold locators.18. An autonomous vehicular appliance according to claim 17 wherein,upon detecting that the received signal exceeds a predetermined limit,the navigation system is arranged to navigate the appliance in adirection to follow a path of substantially equal field strength.
 19. Anautonomous vehicular appliance according to claim 15, wherein thenavigation system includes a light detector for detecting the level ofambient light, memory means for storing information representative ofthe level of ambient light when the autonomous vehicular appliancechanges direction and means for comparing the level of ambient lightwith previously stored information so that the autonomous vehicularappliance can identify when the level of ambient light is the same orsubstantially the same as level previously stored.
 20. An autonomousvehicular appliance according to claim 15, wherein the navigation systemalso comprises a plurality of sensors for detecting obstacles andfeatures of the room.
 21. An autonomous vehicular appliance according toclaim 15, wherein the detection system comprises means for detectingwhen a parameter of the received signals meets a required condition. 22.A method according to claim 21 wherein the appliance is arranged, upondetecting the second type of threshold locator, to prevent itself fromcrossing the part of the boundary marked by the threshold locator untilthe area has been completely traversed by the appliance.
 23. Theappliance of claim 1 or 15, wherein the autonomous vehicular applianceis a robotic floor cleaning device.
 24. The appliance according to claim23, wherein the robotic floor cleaning device is a robotic vacuumcleaner.
 25. A method of cleaning an area using an autonomous vehicularappliance, the method comprising placing at least one each of at leasttwo types of portable threshold locator at locations to define at leastpart of a boundary of an area within which the autonomous vehicularappliance is to be confined at least temporarily and operating theappliance to clean the area, wherein the appliance in operation uses anavigation system to navigate around the area and a detection system toallow the appliance to detect the presence of the portable thresholdlocators, the detection system receiving signals from the thresholdlocators and the appliance using the received locators to detect theparts of the boundary defined by the threshold locators, and upondetecting a first type of threshold locator, prevents itself fromcrossing the part of the boundary worked by the first type of thresholdlocator and, upon detecting a second type of threshold locator, preventsitself from crossing the part of the boundary marked by the second typeof threshold location until a certain condition has been met.
 26. Amethod according to claim 25, wherein the appliance is configured toprevent itself from crossing the part of the boundary marked by thesecond type of threshold locator until the area has been completelytraversed by the appliance.